The present invention relates generally to reinforcement spacers for reinforced concrete structures and, more particularly, to a weldless stirrup spacer for connecting and positioning concentric or parallel reinforcement wire cages in such structures.
Stirrup spacers are conventionally used in double cage reinforced round concrete pipe to position the inner and outer reinforcement cages at the appropriate distance apart and to space the outer reinforcement cage from the outer form surface to provide the required concrete cover. Such spacers typically take the form of a resilient wire member that hooks or snaps over the reinforcement wires. When the stirrup spacers are installed, the inherent resiliency of the outer reinforcement cage tends to apply tensile forces to the spacers to hold them in place. Such tensile forces, however, are not always evenly sufficient to maintain the proper placement of the spacers on the cages in the face of strong dislodging forces during casting. Moreover, conventional stirrup spacers do not prevent displacement of the inner and/or outer reinforcement cages towards one another.
To overcome these problems with conventional stirrup spacers, the spacers are generally tied or welded to the reinforcement wires. Not only are these labor-intensive, time consuming processes, they do not fully solve the problems. In the case of tying, tie wires are relatively weak and can fail and allow displacement of the cages towards each other during pouring of the concrete. Welding, on the other hand, can weaken the reinforcement wires of the cages and/or the spacers, and welding is often not permitted by the product specifications for that reason. Also, in applications where galvanized (zinc coated) reinforcement wires are required, welding volatilizes the zinc and the vapors present a serious toxic health hazard to workers, which is prohibitive.
In addition, certain prior art stirrup spacers are difficult to install on the reinforcement cages, requiring the use of an installation tool and both of the worker""s hands. Such tool-installed spacers are not only difficult and time-consuming to handle, but they can cause injury to the worker in the event the tool slips out of position during installation.
An object of the present invention is to provide a weldless stirrup spacer that can be safely installed manuallyxe2x80x94i.e., by hand without any toolsxe2x80x94and which requires very little force to be applied to it when it is being installed.
Another object is to reduce the costs of producing concrete structures, and precast concrete structures in particular, by eliminating welding or tie-wiring the stirrup spacers to the reinforcement wires and by providing weldless stirrup spacers that are relatively inexpensive and that can be quickly installed, thus saving time and labor costs when the wire reinforcement cages are being assembled within the molds.
It is also an object to provide a weldless stirrup spacer that remains securely in position after installation and especially when the concrete is being poured into the mold.
Still another object is to provide a weldless stirrup spacer that can be manufactured at low cost in one machine operation.
The foregoing and other objects are attained, in accordance with the invention, by the provision of a weldless stirrup spacer which is formed as a unitary resilient wire member having a hook end pigtail portion for engagement with a first reinforcement wire (for example, of an inner reinforcement cage), an elongated spanning portion having an axis of elongation Bxe2x80x94B, and a fastening end for engagement with a second reinforcement wire (for example, of an outer reinforcement cage). The hook end includes a generally corkscrew-shaped pigtail portion extending from a juncture with the spanning portion laterally to one side of the spanning portion along an axis of curvature Axe2x80x94A that is substantially perpendicular to the axis Bxe2x80x94B. As installed on the first reinforcement wire, the pigtail portion engages upwardly, outwardly, downwardly and inwardly facing surfaces of the first reinforcement wire at spaced distances along the axis of curvature Axe2x80x94A. In a preferred embodiment, the pigtail portion includes a curved body portion which lies substantially in a plane Cxe2x80x94C that is inclined at an acute angle to the axis Bxe2x80x94B. The pigtail portion preferably terminates in an upright end portion which extends out of the plane Cxe2x80x94C in the direction away from the central spanning portion. The upright end portion engages inwardly and upwardly facing surfaces of the reinforcement wire.
The fastening end portion includes a detent part which is curved to form a groove at a juncture with the other end of the spanning portion so as, when installed, to engage upwardly, outwardly and downwardly facing surfaces of the second reinforcement wire at a first location along the reinforcement wire, a J-hook part shaped and positioned to form a groove so as to engage upwardly, inwardly and downwardly facing surfaces of the second reinforcement wire at a second location along the reinforcement wire spaced laterally apart from the first location to the same side of the spanning portion as the spiral-shaped main portion of the hook end, and a loop part joining the detent part and the J-hook part. The loop part of the fastening end serves the dual function of spacing the second reinforcement wire at the correct concrete-cover distance from the adjacent mold wall and providing a handgrip to be grasped and hand pushed by a worker during installation of the spacer on the reinforcement wires.
The foregoing configuration of the weldless stirrup spacer affords a number of important advantages relative to prior art stirrup spacers.
The pigtail-shaped hook end provides a unique four-way holding engagement with the first reinforcement wire, thereby restraining the wire against movement in all four principal directions, i.e., upwardly, downwardly, inwardly or outwardly.
The fastening end portion of the spacer locks downwardly onto the second reinforcement wire and, in combination with the hook end portion, secures the first and second reinforcement wires (for example, the inner and outer reinforcement cages) together into a single, strong and positive reinforcement unit.
The spacer can readily be installed on both wires with one hand, without tools and without tying or welding. This capability greatly facilitates installation of the spacer through the outer reinforcement wire cage of reinforced concrete structures such as reinforced concrete pipe.
The tool-less one-handed installation of the spacer avoids the risk of injury associated with the installation of certain prior art spacers because the present invention does not require torsional or twisting forces to fasten it to the reinforcement wires.
As the stirrup spacer of the invention is a single, unitary wire member, it can be economically manufactured, in one machine operation.
The weldless stirrup spacer of the invention thus combines in a single, unitary member ease and safety of attachment, economy of manufacture, and strength and accuracy of installation.
In preferred embodiments, the plane Cxe2x80x94C of the curved main body portion of the hook end is inclined at an acute angle of approximately 60xc2x0xc2x15xc2x0 to the axis of elongation of the spanning portion of the spacer. The upright end portion of the pigtail preferably lies in a plane Dxe2x80x94D that is inclined at an angle of 60xc2x0xc2x15xc2x0 to the axis of curvature Axe2x80x94A of the pigtail portion. Also, the upright end portion preferably terminates at the same elevation as the spanning portion.
The J-hook part of the fastening end portion preferably includes a serpentine distal end leg part, the tip of which forms a camming surface that is adapted to engage an inner surface of the second reinforcement wire and facilitate reception of the second reinforcement wire into the groove of the J-hook part by aiding in causing lateral deflection of the spacer""s fastening end and resilient constriction of the spacer hook portion of the fastening end. The J-hook part and detent part of the fastening end portion form in profile a throat having an entrance that is narrower than the lateral thickness of the second reinforcement wire. The loop part of the fastening end is preferably substantially arcuate in profile, and the outer extremity of the loop part is adapted to engage one form of a mold for a reinforced concrete structure to position the second reinforcement wire in a predetermined position within the mold.